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<pre><span class="sourceLineNo">001</span>/*<a name="line.1"></a>
<span class="sourceLineNo">002</span> * Copyright (C) 2011 The Guava Authors<a name="line.2"></a>
<span class="sourceLineNo">003</span> *<a name="line.3"></a>
<span class="sourceLineNo">004</span> * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except<a name="line.4"></a>
<span class="sourceLineNo">005</span> * in compliance with the License. You may obtain a copy of the License at<a name="line.5"></a>
<span class="sourceLineNo">006</span> *<a name="line.6"></a>
<span class="sourceLineNo">007</span> * http://www.apache.org/licenses/LICENSE-2.0<a name="line.7"></a>
<span class="sourceLineNo">008</span> *<a name="line.8"></a>
<span class="sourceLineNo">009</span> * Unless required by applicable law or agreed to in writing, software distributed under the License<a name="line.9"></a>
<span class="sourceLineNo">010</span> * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express<a name="line.10"></a>
<span class="sourceLineNo">011</span> * or implied. See the License for the specific language governing permissions and limitations under<a name="line.11"></a>
<span class="sourceLineNo">012</span> * the License.<a name="line.12"></a>
<span class="sourceLineNo">013</span> */<a name="line.13"></a>
<span class="sourceLineNo">014</span><a name="line.14"></a>
<span class="sourceLineNo">015</span>package com.google.common.hash;<a name="line.15"></a>
<span class="sourceLineNo">016</span><a name="line.16"></a>
<span class="sourceLineNo">017</span>import static com.google.common.base.Preconditions.checkArgument;<a name="line.17"></a>
<span class="sourceLineNo">018</span><a name="line.18"></a>
<span class="sourceLineNo">019</span>import com.google.common.annotations.Beta;<a name="line.19"></a>
<span class="sourceLineNo">020</span>import com.google.common.annotations.VisibleForTesting;<a name="line.20"></a>
<span class="sourceLineNo">021</span>import com.google.common.base.Supplier;<a name="line.21"></a>
<span class="sourceLineNo">022</span><a name="line.22"></a>
<span class="sourceLineNo">023</span>import java.nio.ByteBuffer;<a name="line.23"></a>
<span class="sourceLineNo">024</span>import java.security.MessageDigest;<a name="line.24"></a>
<span class="sourceLineNo">025</span>import java.util.Iterator;<a name="line.25"></a>
<span class="sourceLineNo">026</span>import java.util.zip.Adler32;<a name="line.26"></a>
<span class="sourceLineNo">027</span>import java.util.zip.CRC32;<a name="line.27"></a>
<span class="sourceLineNo">028</span>import java.util.zip.Checksum;<a name="line.28"></a>
<span class="sourceLineNo">029</span><a name="line.29"></a>
<span class="sourceLineNo">030</span>/**<a name="line.30"></a>
<span class="sourceLineNo">031</span> * Static methods to obtain {@link HashFunction} instances, and other static hashing-related<a name="line.31"></a>
<span class="sourceLineNo">032</span> * utilities.<a name="line.32"></a>
<span class="sourceLineNo">033</span> *<a name="line.33"></a>
<span class="sourceLineNo">034</span> * @author Kevin Bourrillion<a name="line.34"></a>
<span class="sourceLineNo">035</span> * @author Dimitris Andreou<a name="line.35"></a>
<span class="sourceLineNo">036</span> * @author Kurt Alfred Kluever<a name="line.36"></a>
<span class="sourceLineNo">037</span> * @since 11.0<a name="line.37"></a>
<span class="sourceLineNo">038</span> */<a name="line.38"></a>
<span class="sourceLineNo">039</span>@Beta<a name="line.39"></a>
<span class="sourceLineNo">040</span>public final class Hashing {<a name="line.40"></a>
<span class="sourceLineNo">041</span>  private Hashing() {}<a name="line.41"></a>
<span class="sourceLineNo">042</span><a name="line.42"></a>
<span class="sourceLineNo">043</span>  /**<a name="line.43"></a>
<span class="sourceLineNo">044</span>   * Used to randomize {@link #goodFastHash} instances, so that programs which persist anything<a name="line.44"></a>
<span class="sourceLineNo">045</span>   * dependent on hashcodes of those, will fail sooner than later.<a name="line.45"></a>
<span class="sourceLineNo">046</span>   */<a name="line.46"></a>
<span class="sourceLineNo">047</span>  private static final int GOOD_FAST_HASH_SEED = (int) System.currentTimeMillis();<a name="line.47"></a>
<span class="sourceLineNo">048</span><a name="line.48"></a>
<span class="sourceLineNo">049</span>  // Used by goodFastHash when minimumBits == 32.<a name="line.49"></a>
<span class="sourceLineNo">050</span>  private static final HashFunction GOOD_FAST_HASH_FUNCTION_32 = murmur3_32(GOOD_FAST_HASH_SEED);<a name="line.50"></a>
<span class="sourceLineNo">051</span><a name="line.51"></a>
<span class="sourceLineNo">052</span>  // Used by goodFastHash when 32 &lt; minimumBits &lt;= 128.<a name="line.52"></a>
<span class="sourceLineNo">053</span>  private static final HashFunction GOOD_FAST_HASH_FUNCTION_128 = murmur3_128(GOOD_FAST_HASH_SEED);<a name="line.53"></a>
<span class="sourceLineNo">054</span><a name="line.54"></a>
<span class="sourceLineNo">055</span>  /**<a name="line.55"></a>
<span class="sourceLineNo">056</span>   * Returns a general-purpose, &lt;b&gt;non-cryptographic-strength&lt;/b&gt;, streaming hash function that<a name="line.56"></a>
<span class="sourceLineNo">057</span>   * produces hash codes of length at least {@code minimumBits}. Users without specific<a name="line.57"></a>
<span class="sourceLineNo">058</span>   * compatibility requirements and who do not persist the hash codes are encouraged to<a name="line.58"></a>
<span class="sourceLineNo">059</span>   * choose this hash function.<a name="line.59"></a>
<span class="sourceLineNo">060</span>   *<a name="line.60"></a>
<span class="sourceLineNo">061</span>   * &lt;p&gt;Repeated calls to {@link #goodFastHash} with the same {@code minimumBits} value will<a name="line.61"></a>
<span class="sourceLineNo">062</span>   * return {@link HashFunction} instances with identical behavior (but not necessarily the<a name="line.62"></a>
<span class="sourceLineNo">063</span>   * same instance) for the duration of the current virtual machine.<a name="line.63"></a>
<span class="sourceLineNo">064</span>   *<a name="line.64"></a>
<span class="sourceLineNo">065</span>   * &lt;p&gt;&lt;b&gt;Warning: the implementation is unspecified and is subject to change.&lt;/b&gt;<a name="line.65"></a>
<span class="sourceLineNo">066</span>   *<a name="line.66"></a>
<span class="sourceLineNo">067</span>   * @throws IllegalArgumentException if {@code minimumBits} is not positive<a name="line.67"></a>
<span class="sourceLineNo">068</span>   */<a name="line.68"></a>
<span class="sourceLineNo">069</span>  public static HashFunction goodFastHash(int minimumBits) {<a name="line.69"></a>
<span class="sourceLineNo">070</span>    int bits = checkPositiveAndMakeMultipleOf32(minimumBits);<a name="line.70"></a>
<span class="sourceLineNo">071</span><a name="line.71"></a>
<span class="sourceLineNo">072</span>    if (bits == 32) {<a name="line.72"></a>
<span class="sourceLineNo">073</span>      return GOOD_FAST_HASH_FUNCTION_32;<a name="line.73"></a>
<span class="sourceLineNo">074</span>    }<a name="line.74"></a>
<span class="sourceLineNo">075</span>    if (bits &lt;= 128) {<a name="line.75"></a>
<span class="sourceLineNo">076</span>      return GOOD_FAST_HASH_FUNCTION_128;<a name="line.76"></a>
<span class="sourceLineNo">077</span>    }<a name="line.77"></a>
<span class="sourceLineNo">078</span><a name="line.78"></a>
<span class="sourceLineNo">079</span>    // Otherwise, join together some 128-bit murmur3s<a name="line.79"></a>
<span class="sourceLineNo">080</span>    int hashFunctionsNeeded = (bits + 127) / 128;<a name="line.80"></a>
<span class="sourceLineNo">081</span>    HashFunction[] hashFunctions = new HashFunction[hashFunctionsNeeded];<a name="line.81"></a>
<span class="sourceLineNo">082</span>    hashFunctions[0] = GOOD_FAST_HASH_FUNCTION_128;<a name="line.82"></a>
<span class="sourceLineNo">083</span>    int seed = GOOD_FAST_HASH_SEED;<a name="line.83"></a>
<span class="sourceLineNo">084</span>    for (int i = 1; i &lt; hashFunctionsNeeded; i++) {<a name="line.84"></a>
<span class="sourceLineNo">085</span>      seed += 1500450271; // a prime; shouldn't matter<a name="line.85"></a>
<span class="sourceLineNo">086</span>      hashFunctions[i] = murmur3_128(seed);<a name="line.86"></a>
<span class="sourceLineNo">087</span>    }<a name="line.87"></a>
<span class="sourceLineNo">088</span>    return new ConcatenatedHashFunction(hashFunctions);<a name="line.88"></a>
<span class="sourceLineNo">089</span>  }<a name="line.89"></a>
<span class="sourceLineNo">090</span><a name="line.90"></a>
<span class="sourceLineNo">091</span>  /**<a name="line.91"></a>
<span class="sourceLineNo">092</span>   * Returns a hash function implementing the<a name="line.92"></a>
<span class="sourceLineNo">093</span>   * &lt;a href="http://smhasher.googlecode.com/svn/trunk/MurmurHash3.cpp"&gt;<a name="line.93"></a>
<span class="sourceLineNo">094</span>   * 32-bit murmur3 algorithm, x86 variant&lt;/a&gt; (little-endian variant),<a name="line.94"></a>
<span class="sourceLineNo">095</span>   * using the given seed value.<a name="line.95"></a>
<span class="sourceLineNo">096</span>   *<a name="line.96"></a>
<span class="sourceLineNo">097</span>   * &lt;p&gt;The exact C++ equivalent is the MurmurHash3_x86_32 function (Murmur3A).<a name="line.97"></a>
<span class="sourceLineNo">098</span>   */<a name="line.98"></a>
<span class="sourceLineNo">099</span>  public static HashFunction murmur3_32(int seed) {<a name="line.99"></a>
<span class="sourceLineNo">100</span>    return new Murmur3_32HashFunction(seed);<a name="line.100"></a>
<span class="sourceLineNo">101</span>  }<a name="line.101"></a>
<span class="sourceLineNo">102</span><a name="line.102"></a>
<span class="sourceLineNo">103</span>  /**<a name="line.103"></a>
<span class="sourceLineNo">104</span>   * Returns a hash function implementing the<a name="line.104"></a>
<span class="sourceLineNo">105</span>   * &lt;a href="http://smhasher.googlecode.com/svn/trunk/MurmurHash3.cpp"&gt;<a name="line.105"></a>
<span class="sourceLineNo">106</span>   * 32-bit murmur3 algorithm, x86 variant&lt;/a&gt; (little-endian variant),<a name="line.106"></a>
<span class="sourceLineNo">107</span>   * using a seed value of zero.<a name="line.107"></a>
<span class="sourceLineNo">108</span>   *<a name="line.108"></a>
<span class="sourceLineNo">109</span>   * &lt;p&gt;The exact C++ equivalent is the MurmurHash3_x86_32 function (Murmur3A).<a name="line.109"></a>
<span class="sourceLineNo">110</span>   */<a name="line.110"></a>
<span class="sourceLineNo">111</span>  public static HashFunction murmur3_32() {<a name="line.111"></a>
<span class="sourceLineNo">112</span>    return MURMUR3_32;<a name="line.112"></a>
<span class="sourceLineNo">113</span>  }<a name="line.113"></a>
<span class="sourceLineNo">114</span><a name="line.114"></a>
<span class="sourceLineNo">115</span>  private static final Murmur3_32HashFunction MURMUR3_32 = new Murmur3_32HashFunction(0);<a name="line.115"></a>
<span class="sourceLineNo">116</span><a name="line.116"></a>
<span class="sourceLineNo">117</span>  /**<a name="line.117"></a>
<span class="sourceLineNo">118</span>   * Returns a hash function implementing the<a name="line.118"></a>
<span class="sourceLineNo">119</span>   * &lt;a href="http://smhasher.googlecode.com/svn/trunk/MurmurHash3.cpp"&gt;<a name="line.119"></a>
<span class="sourceLineNo">120</span>   * 128-bit murmur3 algorithm, x64 variant&lt;/a&gt; (little-endian variant),<a name="line.120"></a>
<span class="sourceLineNo">121</span>   * using the given seed value.<a name="line.121"></a>
<span class="sourceLineNo">122</span>   *<a name="line.122"></a>
<span class="sourceLineNo">123</span>   * &lt;p&gt;The exact C++ equivalent is the MurmurHash3_x64_128 function (Murmur3F).<a name="line.123"></a>
<span class="sourceLineNo">124</span>   */<a name="line.124"></a>
<span class="sourceLineNo">125</span>  public static HashFunction murmur3_128(int seed) {<a name="line.125"></a>
<span class="sourceLineNo">126</span>    return new Murmur3_128HashFunction(seed);<a name="line.126"></a>
<span class="sourceLineNo">127</span>  }<a name="line.127"></a>
<span class="sourceLineNo">128</span><a name="line.128"></a>
<span class="sourceLineNo">129</span>  /**<a name="line.129"></a>
<span class="sourceLineNo">130</span>   * Returns a hash function implementing the<a name="line.130"></a>
<span class="sourceLineNo">131</span>   * &lt;a href="http://smhasher.googlecode.com/svn/trunk/MurmurHash3.cpp"&gt;<a name="line.131"></a>
<span class="sourceLineNo">132</span>   * 128-bit murmur3 algorithm, x64 variant&lt;/a&gt; (little-endian variant),<a name="line.132"></a>
<span class="sourceLineNo">133</span>   * using a seed value of zero.<a name="line.133"></a>
<span class="sourceLineNo">134</span>   *<a name="line.134"></a>
<span class="sourceLineNo">135</span>   * &lt;p&gt;The exact C++ equivalent is the MurmurHash3_x64_128 function (Murmur3F).<a name="line.135"></a>
<span class="sourceLineNo">136</span>   */<a name="line.136"></a>
<span class="sourceLineNo">137</span>  public static HashFunction murmur3_128() {<a name="line.137"></a>
<span class="sourceLineNo">138</span>    return MURMUR3_128;<a name="line.138"></a>
<span class="sourceLineNo">139</span>  }<a name="line.139"></a>
<span class="sourceLineNo">140</span><a name="line.140"></a>
<span class="sourceLineNo">141</span>  private static final Murmur3_128HashFunction MURMUR3_128 = new Murmur3_128HashFunction(0);<a name="line.141"></a>
<span class="sourceLineNo">142</span><a name="line.142"></a>
<span class="sourceLineNo">143</span>  /**<a name="line.143"></a>
<span class="sourceLineNo">144</span>   * Returns a hash function implementing the MD5 hash algorithm (128 hash bits) by delegating to<a name="line.144"></a>
<span class="sourceLineNo">145</span>   * the MD5 {@link MessageDigest}.<a name="line.145"></a>
<span class="sourceLineNo">146</span>   */<a name="line.146"></a>
<span class="sourceLineNo">147</span>  public static HashFunction md5() {<a name="line.147"></a>
<span class="sourceLineNo">148</span>    return MD5;<a name="line.148"></a>
<span class="sourceLineNo">149</span>  }<a name="line.149"></a>
<span class="sourceLineNo">150</span><a name="line.150"></a>
<span class="sourceLineNo">151</span>  private static final HashFunction MD5 = new MessageDigestHashFunction("MD5");<a name="line.151"></a>
<span class="sourceLineNo">152</span><a name="line.152"></a>
<span class="sourceLineNo">153</span>  /**<a name="line.153"></a>
<span class="sourceLineNo">154</span>   * Returns a hash function implementing the SHA-1 algorithm (160 hash bits) by delegating to the<a name="line.154"></a>
<span class="sourceLineNo">155</span>   * SHA-1 {@link MessageDigest}.<a name="line.155"></a>
<span class="sourceLineNo">156</span>   */<a name="line.156"></a>
<span class="sourceLineNo">157</span>  public static HashFunction sha1() {<a name="line.157"></a>
<span class="sourceLineNo">158</span>    return SHA_1;<a name="line.158"></a>
<span class="sourceLineNo">159</span>  }<a name="line.159"></a>
<span class="sourceLineNo">160</span><a name="line.160"></a>
<span class="sourceLineNo">161</span>  private static final HashFunction SHA_1 = new MessageDigestHashFunction("SHA-1");<a name="line.161"></a>
<span class="sourceLineNo">162</span><a name="line.162"></a>
<span class="sourceLineNo">163</span>  /**<a name="line.163"></a>
<span class="sourceLineNo">164</span>   * Returns a hash function implementing the SHA-256 algorithm (256 hash bits) by delegating to<a name="line.164"></a>
<span class="sourceLineNo">165</span>   * the SHA-256 {@link MessageDigest}.<a name="line.165"></a>
<span class="sourceLineNo">166</span>   */<a name="line.166"></a>
<span class="sourceLineNo">167</span>  public static HashFunction sha256() {<a name="line.167"></a>
<span class="sourceLineNo">168</span>    return SHA_256;<a name="line.168"></a>
<span class="sourceLineNo">169</span>  }<a name="line.169"></a>
<span class="sourceLineNo">170</span><a name="line.170"></a>
<span class="sourceLineNo">171</span>  private static final HashFunction SHA_256 = new MessageDigestHashFunction("SHA-256");<a name="line.171"></a>
<span class="sourceLineNo">172</span><a name="line.172"></a>
<span class="sourceLineNo">173</span>  /**<a name="line.173"></a>
<span class="sourceLineNo">174</span>   * Returns a hash function implementing the SHA-512 algorithm (512 hash bits) by delegating to the<a name="line.174"></a>
<span class="sourceLineNo">175</span>   * SHA-512 {@link MessageDigest}.<a name="line.175"></a>
<span class="sourceLineNo">176</span>   */<a name="line.176"></a>
<span class="sourceLineNo">177</span>  public static HashFunction sha512() {<a name="line.177"></a>
<span class="sourceLineNo">178</span>    return SHA_512;<a name="line.178"></a>
<span class="sourceLineNo">179</span>  }<a name="line.179"></a>
<span class="sourceLineNo">180</span><a name="line.180"></a>
<span class="sourceLineNo">181</span>  private static final HashFunction SHA_512 = new MessageDigestHashFunction("SHA-512");<a name="line.181"></a>
<span class="sourceLineNo">182</span><a name="line.182"></a>
<span class="sourceLineNo">183</span>  /**<a name="line.183"></a>
<span class="sourceLineNo">184</span>   * Returns a hash function implementing the CRC-32 checksum algorithm (32 hash bits) by delegating<a name="line.184"></a>
<span class="sourceLineNo">185</span>   * to the {@link CRC32} {@link Checksum}.<a name="line.185"></a>
<span class="sourceLineNo">186</span>   *<a name="line.186"></a>
<span class="sourceLineNo">187</span>   * &lt;p&gt;To get the {@code long} value equivalent to {@link Checksum#getValue()} for a<a name="line.187"></a>
<span class="sourceLineNo">188</span>   * {@code HashCode} produced by this function, use {@link HashCode#padToLong()}.<a name="line.188"></a>
<span class="sourceLineNo">189</span>   *<a name="line.189"></a>
<span class="sourceLineNo">190</span>   * @since 14.0<a name="line.190"></a>
<span class="sourceLineNo">191</span>   */<a name="line.191"></a>
<span class="sourceLineNo">192</span>  public static HashFunction crc32() {<a name="line.192"></a>
<span class="sourceLineNo">193</span>    return CRC_32;<a name="line.193"></a>
<span class="sourceLineNo">194</span>  }<a name="line.194"></a>
<span class="sourceLineNo">195</span><a name="line.195"></a>
<span class="sourceLineNo">196</span>  private static final HashFunction CRC_32 = checksumHashFunction(ChecksumType.CRC_32);<a name="line.196"></a>
<span class="sourceLineNo">197</span><a name="line.197"></a>
<span class="sourceLineNo">198</span>  /**<a name="line.198"></a>
<span class="sourceLineNo">199</span>   * Returns a hash function implementing the Adler-32 checksum algorithm (32 hash bits) by<a name="line.199"></a>
<span class="sourceLineNo">200</span>   * delegating to the {@link Adler32} {@link Checksum}.<a name="line.200"></a>
<span class="sourceLineNo">201</span>   *<a name="line.201"></a>
<span class="sourceLineNo">202</span>   * &lt;p&gt;To get the {@code long} value equivalent to {@link Checksum#getValue()} for a<a name="line.202"></a>
<span class="sourceLineNo">203</span>   * {@code HashCode} produced by this function, use {@link HashCode#padToLong()}.<a name="line.203"></a>
<span class="sourceLineNo">204</span>   *<a name="line.204"></a>
<span class="sourceLineNo">205</span>   * @since 14.0<a name="line.205"></a>
<span class="sourceLineNo">206</span>   */<a name="line.206"></a>
<span class="sourceLineNo">207</span>  public static HashFunction adler32() {<a name="line.207"></a>
<span class="sourceLineNo">208</span>    return ADLER_32;<a name="line.208"></a>
<span class="sourceLineNo">209</span>  }<a name="line.209"></a>
<span class="sourceLineNo">210</span><a name="line.210"></a>
<span class="sourceLineNo">211</span>  private static final HashFunction ADLER_32 = checksumHashFunction(ChecksumType.ADLER_32);<a name="line.211"></a>
<span class="sourceLineNo">212</span><a name="line.212"></a>
<span class="sourceLineNo">213</span>  private static HashFunction checksumHashFunction(ChecksumType type) {<a name="line.213"></a>
<span class="sourceLineNo">214</span>    return new ChecksumHashFunction(type, type.bits);<a name="line.214"></a>
<span class="sourceLineNo">215</span>  }<a name="line.215"></a>
<span class="sourceLineNo">216</span><a name="line.216"></a>
<span class="sourceLineNo">217</span>  enum ChecksumType implements Supplier&lt;Checksum&gt; {<a name="line.217"></a>
<span class="sourceLineNo">218</span>    CRC_32(32) {<a name="line.218"></a>
<span class="sourceLineNo">219</span>      @Override<a name="line.219"></a>
<span class="sourceLineNo">220</span>      public Checksum get() {<a name="line.220"></a>
<span class="sourceLineNo">221</span>        return new CRC32();<a name="line.221"></a>
<span class="sourceLineNo">222</span>      }<a name="line.222"></a>
<span class="sourceLineNo">223</span>    },<a name="line.223"></a>
<span class="sourceLineNo">224</span>    ADLER_32(32) {<a name="line.224"></a>
<span class="sourceLineNo">225</span>      @Override<a name="line.225"></a>
<span class="sourceLineNo">226</span>      public Checksum get() {<a name="line.226"></a>
<span class="sourceLineNo">227</span>        return new Adler32();<a name="line.227"></a>
<span class="sourceLineNo">228</span>      }<a name="line.228"></a>
<span class="sourceLineNo">229</span>    };<a name="line.229"></a>
<span class="sourceLineNo">230</span><a name="line.230"></a>
<span class="sourceLineNo">231</span>    private final int bits;<a name="line.231"></a>
<span class="sourceLineNo">232</span><a name="line.232"></a>
<span class="sourceLineNo">233</span>    ChecksumType(int bits) {<a name="line.233"></a>
<span class="sourceLineNo">234</span>      this.bits = bits;<a name="line.234"></a>
<span class="sourceLineNo">235</span>    }<a name="line.235"></a>
<span class="sourceLineNo">236</span><a name="line.236"></a>
<span class="sourceLineNo">237</span>    @Override<a name="line.237"></a>
<span class="sourceLineNo">238</span>    public abstract Checksum get();<a name="line.238"></a>
<span class="sourceLineNo">239</span>  }<a name="line.239"></a>
<span class="sourceLineNo">240</span><a name="line.240"></a>
<span class="sourceLineNo">241</span>  // Lazy initialization holder class idiom.<a name="line.241"></a>
<span class="sourceLineNo">242</span><a name="line.242"></a>
<span class="sourceLineNo">243</span>  /**<a name="line.243"></a>
<span class="sourceLineNo">244</span>   * If {@code hashCode} has enough bits, returns {@code hashCode.asLong()}, otherwise<a name="line.244"></a>
<span class="sourceLineNo">245</span>   * returns a {@code long} value with {@code hashCode.asInt()} as the least-significant<a name="line.245"></a>
<span class="sourceLineNo">246</span>   * four bytes and {@code 0x00} as each of the most-significant four bytes.<a name="line.246"></a>
<span class="sourceLineNo">247</span>   *<a name="line.247"></a>
<span class="sourceLineNo">248</span>   * @deprecated Use {@code HashCode.padToLong()} instead. This method is scheduled to be<a name="line.248"></a>
<span class="sourceLineNo">249</span>   *     removed in Guava 15.0.<a name="line.249"></a>
<span class="sourceLineNo">250</span>   */<a name="line.250"></a>
<span class="sourceLineNo">251</span>  @Deprecated<a name="line.251"></a>
<span class="sourceLineNo">252</span>  public static long padToLong(HashCode hashCode) {<a name="line.252"></a>
<span class="sourceLineNo">253</span>    return hashCode.padToLong();<a name="line.253"></a>
<span class="sourceLineNo">254</span>  }<a name="line.254"></a>
<span class="sourceLineNo">255</span><a name="line.255"></a>
<span class="sourceLineNo">256</span>  /**<a name="line.256"></a>
<span class="sourceLineNo">257</span>   * Assigns to {@code hashCode} a "bucket" in the range {@code [0, buckets)}, in a uniform<a name="line.257"></a>
<span class="sourceLineNo">258</span>   * manner that minimizes the need for remapping as {@code buckets} grows. That is,<a name="line.258"></a>
<span class="sourceLineNo">259</span>   * {@code consistentHash(h, n)} equals:<a name="line.259"></a>
<span class="sourceLineNo">260</span>   *<a name="line.260"></a>
<span class="sourceLineNo">261</span>   * &lt;ul&gt;<a name="line.261"></a>
<span class="sourceLineNo">262</span>   * &lt;li&gt;{@code n - 1}, with approximate probability {@code 1/n}<a name="line.262"></a>
<span class="sourceLineNo">263</span>   * &lt;li&gt;{@code consistentHash(h, n - 1)}, otherwise (probability {@code 1 - 1/n})<a name="line.263"></a>
<span class="sourceLineNo">264</span>   * &lt;/ul&gt;<a name="line.264"></a>
<span class="sourceLineNo">265</span>   *<a name="line.265"></a>
<span class="sourceLineNo">266</span>   * &lt;p&gt;See the &lt;a href="http://en.wikipedia.org/wiki/Consistent_hashing"&gt;wikipedia<a name="line.266"></a>
<span class="sourceLineNo">267</span>   * article on consistent hashing&lt;/a&gt; for more information.<a name="line.267"></a>
<span class="sourceLineNo">268</span>   * &lt;p&gt;<a name="line.268"></a>
<span class="sourceLineNo">269</span>   * If you might want to have weights for the buckets in the future, take a look at<a name="line.269"></a>
<span class="sourceLineNo">270</span>   * {@code weightedConsistentHash}.<a name="line.270"></a>
<span class="sourceLineNo">271</span>   */<a name="line.271"></a>
<span class="sourceLineNo">272</span>  public static int consistentHash(HashCode hashCode, int buckets) {<a name="line.272"></a>
<span class="sourceLineNo">273</span>    return consistentHash(hashCode.padToLong(), buckets);<a name="line.273"></a>
<span class="sourceLineNo">274</span>  }<a name="line.274"></a>
<span class="sourceLineNo">275</span><a name="line.275"></a>
<span class="sourceLineNo">276</span>  /**<a name="line.276"></a>
<span class="sourceLineNo">277</span>   * Assigns to {@code input} a "bucket" in the range {@code [0, buckets)}, in a uniform<a name="line.277"></a>
<span class="sourceLineNo">278</span>   * manner that minimizes the need for remapping as {@code buckets} grows. That is,<a name="line.278"></a>
<span class="sourceLineNo">279</span>   * {@code consistentHash(h, n)} equals:<a name="line.279"></a>
<span class="sourceLineNo">280</span>   *<a name="line.280"></a>
<span class="sourceLineNo">281</span>   * &lt;ul&gt;<a name="line.281"></a>
<span class="sourceLineNo">282</span>   * &lt;li&gt;{@code n - 1}, with approximate probability {@code 1/n}<a name="line.282"></a>
<span class="sourceLineNo">283</span>   * &lt;li&gt;{@code consistentHash(h, n - 1)}, otherwise (probability {@code 1 - 1/n})<a name="line.283"></a>
<span class="sourceLineNo">284</span>   * &lt;/ul&gt;<a name="line.284"></a>
<span class="sourceLineNo">285</span>   *<a name="line.285"></a>
<span class="sourceLineNo">286</span>   * &lt;p&gt;See the &lt;a href="http://en.wikipedia.org/wiki/Consistent_hashing"&gt;wikipedia<a name="line.286"></a>
<span class="sourceLineNo">287</span>   * article on consistent hashing&lt;/a&gt; for more information.<a name="line.287"></a>
<span class="sourceLineNo">288</span>   * &lt;p&gt;<a name="line.288"></a>
<span class="sourceLineNo">289</span>   * If you might want to have weights for the buckets in the future, take a look at<a name="line.289"></a>
<span class="sourceLineNo">290</span>   * {@code weightedConsistentHash}.<a name="line.290"></a>
<span class="sourceLineNo">291</span>   */<a name="line.291"></a>
<span class="sourceLineNo">292</span>  public static int consistentHash(long input, int buckets) {<a name="line.292"></a>
<span class="sourceLineNo">293</span>    checkArgument(buckets &gt; 0, "buckets must be positive: %s", buckets);<a name="line.293"></a>
<span class="sourceLineNo">294</span>    LinearCongruentialGenerator generator = new LinearCongruentialGenerator(input);<a name="line.294"></a>
<span class="sourceLineNo">295</span>    int candidate = 0;<a name="line.295"></a>
<span class="sourceLineNo">296</span>    int next;<a name="line.296"></a>
<span class="sourceLineNo">297</span><a name="line.297"></a>
<span class="sourceLineNo">298</span>    // Jump from bucket to bucket until we go out of range<a name="line.298"></a>
<span class="sourceLineNo">299</span>    while (true) {<a name="line.299"></a>
<span class="sourceLineNo">300</span>      next = (int) ((candidate + 1) / generator.nextDouble());<a name="line.300"></a>
<span class="sourceLineNo">301</span>      if (next &gt;= 0 &amp;&amp; next &lt; buckets) {<a name="line.301"></a>
<span class="sourceLineNo">302</span>        candidate = next;<a name="line.302"></a>
<span class="sourceLineNo">303</span>      } else {<a name="line.303"></a>
<span class="sourceLineNo">304</span>        return candidate;<a name="line.304"></a>
<span class="sourceLineNo">305</span>      }<a name="line.305"></a>
<span class="sourceLineNo">306</span>    }<a name="line.306"></a>
<span class="sourceLineNo">307</span>  }<a name="line.307"></a>
<span class="sourceLineNo">308</span><a name="line.308"></a>
<span class="sourceLineNo">309</span>  /**<a name="line.309"></a>
<span class="sourceLineNo">310</span>   * Returns a hash code, having the same bit length as each of the input hash codes,<a name="line.310"></a>
<span class="sourceLineNo">311</span>   * that combines the information of these hash codes in an ordered fashion. That<a name="line.311"></a>
<span class="sourceLineNo">312</span>   * is, whenever two equal hash codes are produced by two calls to this method, it<a name="line.312"></a>
<span class="sourceLineNo">313</span>   * is &lt;i&gt;as likely as possible&lt;/i&gt; that each was computed from the &lt;i&gt;same&lt;/i&gt;<a name="line.313"></a>
<span class="sourceLineNo">314</span>   * input hash codes in the &lt;i&gt;same&lt;/i&gt; order.<a name="line.314"></a>
<span class="sourceLineNo">315</span>   *<a name="line.315"></a>
<span class="sourceLineNo">316</span>   * @throws IllegalArgumentException if {@code hashCodes} is empty, or the hash codes<a name="line.316"></a>
<span class="sourceLineNo">317</span>   *     do not all have the same bit length<a name="line.317"></a>
<span class="sourceLineNo">318</span>   */<a name="line.318"></a>
<span class="sourceLineNo">319</span>  public static HashCode combineOrdered(Iterable&lt;HashCode&gt; hashCodes) {<a name="line.319"></a>
<span class="sourceLineNo">320</span>    Iterator&lt;HashCode&gt; iterator = hashCodes.iterator();<a name="line.320"></a>
<span class="sourceLineNo">321</span>    checkArgument(iterator.hasNext(), "Must be at least 1 hash code to combine.");<a name="line.321"></a>
<span class="sourceLineNo">322</span>    int bits = iterator.next().bits();<a name="line.322"></a>
<span class="sourceLineNo">323</span>    byte[] resultBytes = new byte[bits / 8];<a name="line.323"></a>
<span class="sourceLineNo">324</span>    for (HashCode hashCode : hashCodes) {<a name="line.324"></a>
<span class="sourceLineNo">325</span>      byte[] nextBytes = hashCode.asBytes();<a name="line.325"></a>
<span class="sourceLineNo">326</span>      checkArgument(nextBytes.length == resultBytes.length,<a name="line.326"></a>
<span class="sourceLineNo">327</span>          "All hashcodes must have the same bit length.");<a name="line.327"></a>
<span class="sourceLineNo">328</span>      for (int i = 0; i &lt; nextBytes.length; i++) {<a name="line.328"></a>
<span class="sourceLineNo">329</span>        resultBytes[i] = (byte) (resultBytes[i] * 37 ^ nextBytes[i]);<a name="line.329"></a>
<span class="sourceLineNo">330</span>      }<a name="line.330"></a>
<span class="sourceLineNo">331</span>    }<a name="line.331"></a>
<span class="sourceLineNo">332</span>    return HashCodes.fromBytesNoCopy(resultBytes);<a name="line.332"></a>
<span class="sourceLineNo">333</span>  }<a name="line.333"></a>
<span class="sourceLineNo">334</span><a name="line.334"></a>
<span class="sourceLineNo">335</span>  /**<a name="line.335"></a>
<span class="sourceLineNo">336</span>   * Returns a hash code, having the same bit length as each of the input hash codes,<a name="line.336"></a>
<span class="sourceLineNo">337</span>   * that combines the information of these hash codes in an unordered fashion. That<a name="line.337"></a>
<span class="sourceLineNo">338</span>   * is, whenever two equal hash codes are produced by two calls to this method, it<a name="line.338"></a>
<span class="sourceLineNo">339</span>   * is &lt;i&gt;as likely as possible&lt;/i&gt; that each was computed from the &lt;i&gt;same&lt;/i&gt;<a name="line.339"></a>
<span class="sourceLineNo">340</span>   * input hash codes in &lt;i&gt;some&lt;/i&gt; order.<a name="line.340"></a>
<span class="sourceLineNo">341</span>   *<a name="line.341"></a>
<span class="sourceLineNo">342</span>   * @throws IllegalArgumentException if {@code hashCodes} is empty, or the hash codes<a name="line.342"></a>
<span class="sourceLineNo">343</span>   *     do not all have the same bit length<a name="line.343"></a>
<span class="sourceLineNo">344</span>   */<a name="line.344"></a>
<span class="sourceLineNo">345</span>  public static HashCode combineUnordered(Iterable&lt;HashCode&gt; hashCodes) {<a name="line.345"></a>
<span class="sourceLineNo">346</span>    Iterator&lt;HashCode&gt; iterator = hashCodes.iterator();<a name="line.346"></a>
<span class="sourceLineNo">347</span>    checkArgument(iterator.hasNext(), "Must be at least 1 hash code to combine.");<a name="line.347"></a>
<span class="sourceLineNo">348</span>    byte[] resultBytes = new byte[iterator.next().bits() / 8];<a name="line.348"></a>
<span class="sourceLineNo">349</span>    for (HashCode hashCode : hashCodes) {<a name="line.349"></a>
<span class="sourceLineNo">350</span>      byte[] nextBytes = hashCode.asBytes();<a name="line.350"></a>
<span class="sourceLineNo">351</span>      checkArgument(nextBytes.length == resultBytes.length,<a name="line.351"></a>
<span class="sourceLineNo">352</span>          "All hashcodes must have the same bit length.");<a name="line.352"></a>
<span class="sourceLineNo">353</span>      for (int i = 0; i &lt; nextBytes.length; i++) {<a name="line.353"></a>
<span class="sourceLineNo">354</span>        resultBytes[i] += nextBytes[i];<a name="line.354"></a>
<span class="sourceLineNo">355</span>      }<a name="line.355"></a>
<span class="sourceLineNo">356</span>    }<a name="line.356"></a>
<span class="sourceLineNo">357</span>    return HashCodes.fromBytesNoCopy(resultBytes);<a name="line.357"></a>
<span class="sourceLineNo">358</span>  }<a name="line.358"></a>
<span class="sourceLineNo">359</span><a name="line.359"></a>
<span class="sourceLineNo">360</span>  /**<a name="line.360"></a>
<span class="sourceLineNo">361</span>   * Checks that the passed argument is positive, and ceils it to a multiple of 32.<a name="line.361"></a>
<span class="sourceLineNo">362</span>   */<a name="line.362"></a>
<span class="sourceLineNo">363</span>  static int checkPositiveAndMakeMultipleOf32(int bits) {<a name="line.363"></a>
<span class="sourceLineNo">364</span>    checkArgument(bits &gt; 0, "Number of bits must be positive");<a name="line.364"></a>
<span class="sourceLineNo">365</span>    return (bits + 31) &amp; ~31;<a name="line.365"></a>
<span class="sourceLineNo">366</span>  }<a name="line.366"></a>
<span class="sourceLineNo">367</span><a name="line.367"></a>
<span class="sourceLineNo">368</span>  // TODO(kevinb): Maybe expose this class via a static Hashing method?<a name="line.368"></a>
<span class="sourceLineNo">369</span>  @VisibleForTesting<a name="line.369"></a>
<span class="sourceLineNo">370</span>  static final class ConcatenatedHashFunction extends AbstractCompositeHashFunction {<a name="line.370"></a>
<span class="sourceLineNo">371</span>    private final int bits;<a name="line.371"></a>
<span class="sourceLineNo">372</span><a name="line.372"></a>
<span class="sourceLineNo">373</span>    ConcatenatedHashFunction(HashFunction... functions) {<a name="line.373"></a>
<span class="sourceLineNo">374</span>      super(functions);<a name="line.374"></a>
<span class="sourceLineNo">375</span>      int bitSum = 0;<a name="line.375"></a>
<span class="sourceLineNo">376</span>      for (HashFunction function : functions) {<a name="line.376"></a>
<span class="sourceLineNo">377</span>        bitSum += function.bits();<a name="line.377"></a>
<span class="sourceLineNo">378</span>      }<a name="line.378"></a>
<span class="sourceLineNo">379</span>      this.bits = bitSum;<a name="line.379"></a>
<span class="sourceLineNo">380</span>    }<a name="line.380"></a>
<span class="sourceLineNo">381</span><a name="line.381"></a>
<span class="sourceLineNo">382</span>    @Override<a name="line.382"></a>
<span class="sourceLineNo">383</span>    HashCode makeHash(Hasher[] hashers) {<a name="line.383"></a>
<span class="sourceLineNo">384</span>      // TODO(user): Get rid of the ByteBuffer here?<a name="line.384"></a>
<span class="sourceLineNo">385</span>      byte[] bytes = new byte[bits / 8];<a name="line.385"></a>
<span class="sourceLineNo">386</span>      ByteBuffer buffer = ByteBuffer.wrap(bytes);<a name="line.386"></a>
<span class="sourceLineNo">387</span>      for (Hasher hasher : hashers) {<a name="line.387"></a>
<span class="sourceLineNo">388</span>        buffer.put(hasher.hash().asBytes());<a name="line.388"></a>
<span class="sourceLineNo">389</span>      }<a name="line.389"></a>
<span class="sourceLineNo">390</span>      return HashCodes.fromBytesNoCopy(bytes);<a name="line.390"></a>
<span class="sourceLineNo">391</span>    }<a name="line.391"></a>
<span class="sourceLineNo">392</span><a name="line.392"></a>
<span class="sourceLineNo">393</span>    @Override<a name="line.393"></a>
<span class="sourceLineNo">394</span>    public int bits() {<a name="line.394"></a>
<span class="sourceLineNo">395</span>      return bits;<a name="line.395"></a>
<span class="sourceLineNo">396</span>    }<a name="line.396"></a>
<span class="sourceLineNo">397</span>  }<a name="line.397"></a>
<span class="sourceLineNo">398</span><a name="line.398"></a>
<span class="sourceLineNo">399</span>  private static final class LinearCongruentialGenerator {<a name="line.399"></a>
<span class="sourceLineNo">400</span>    private long state;<a name="line.400"></a>
<span class="sourceLineNo">401</span><a name="line.401"></a>
<span class="sourceLineNo">402</span>    public LinearCongruentialGenerator(long seed) {<a name="line.402"></a>
<span class="sourceLineNo">403</span>      this.state = seed;<a name="line.403"></a>
<span class="sourceLineNo">404</span>    }<a name="line.404"></a>
<span class="sourceLineNo">405</span><a name="line.405"></a>
<span class="sourceLineNo">406</span>    public double nextDouble() {<a name="line.406"></a>
<span class="sourceLineNo">407</span>      state = 2862933555777941757L * state + 1;<a name="line.407"></a>
<span class="sourceLineNo">408</span>      return ((double) ((int) (state &gt;&gt;&gt; 33) + 1)) / (0x1.0p31);<a name="line.408"></a>
<span class="sourceLineNo">409</span>    }<a name="line.409"></a>
<span class="sourceLineNo">410</span>  }<a name="line.410"></a>
<span class="sourceLineNo">411</span>}<a name="line.411"></a>




























































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